The present invention is directed generally to an improved fluid bed furnace and more particularly to a new and improved pilot light assembly for use in a fluid bed furnace.
Furnaces for heat-treating metal components or the like are well known. Such furnaces have included a heated bath taking the form of molten salt or lead. The molten salt or lead is heated to an elevated temperature and the metal components to be treated are emersed therein, whereupon, the heat of the baths is transferred to the metal components for treatment.
Such furnaces, while being generally successful in heat-treating metal components or the like, have exhibited certain difficulties. For example, molten salt is hazardous when employed because it is potentially explosive should water come into contact with the heated salt. The salt may be heated to a temperature of, for example, 1400.degree.-2000.degree. F., which, upon contacting water, will explode. Hence, a great deal of care is necessary when employing such a furnace to make sure that water does not come into contact with the molten salt.
In the case of molten lead baths, molten lead is extremely acidic in nature, and hence, it is difficult to use in terms of finding a suitable container in which to contain the molten lead. Furthermore, molten lead and salt are wetting materials which, as a result, wet the metallic component being heat treated. As a result, some means must be provided for removing the molten lead or salt bath materials from the components subsequent to being treated.
In view of the foregoing, a furnace for heat-treating metal components or the like has been proposed which does not include salt or lead baths. In contrast, this type of furnace utilized fluidizable material which may take the form of corrundum of silica particles. One material which becomes fluidized upon being subjected to a flow of gas and which has become popular for such use is sand.
Such furnaces have become known as fluid bed furnaces, and one such furnace is fully described in U.S. Pat. No. 3,884,617, which patent is incorporated herein by reference. The fluid bed furnace there disclosed includes a fluid bed which includes fluidizable material, such as particulate sand. A burner disposed beneath the fluid bed distributes a heated gas mixture to the fluidizable material within the fluid bed for fluidizing and agitating the fluid bed particles. As a result, the heat of the gas mixute is transferred to the fluidizable material and the heat of the fluidizable material is in turn transferred to metallic components placed therein for heat treatment.
Agitation of the fluidized material particles provides for continuous mixing of the particles and continuous particle flow within the fluid bed for obtaining heat from the gas mixture. Fluid bed furnaces have become attractive for heat treating metallic components because the fluidizable material is inert and non-explosive when contacting water. Furthermore, due to the inert nature of the fluidizable material, the fluidizable material does not attack the walls of the container in which it is held. Lastly, the fluidizable material is non-wetting negating the need for treating the heat-treated components for removal of the fluidizable material therefrom.
The burner of the fluid bed furnace is usually provided beneath the fluid bed and is arranged to burn a fuel mixture to provide the flow of gas mixture at an elevated temperature for fluidizing and heating the fluidizable material. In order to ignite such a furnace, the fuel mixture supplied to the burner is allowed to flow through the fluidizable material. Before the supply of fuel mixture is provided to the burner, an ignition flame must be provided above the fluidizable material within the fluid bed. Upon reaching the ignition flame, the fuel mixture will ignite for igniting the burner. After the fuel mixture within the fluidizable material is fully combusted, the burner provides the gas mixture to the fluid bed at an elevated temperature. The flow of the gas mixture fluidizes the fluid bed and the heat of the gas mixture heats the fluidizable material within the fluid bed.
In order to achieve reliable ignition of the fluid bed furnace burner, a flame relatively substantial in length is necessary to be produced in the fluid bed. Furthermore, in order to avoid explosions, the ignition flame must be provided before the fuel mixture is supplied to the burner. Therefore, a pilot light for such a furnace must not only provide an ignition or pilot flame of substantial length within the fluid bed, but furthermore, must include means for sensing the presence of the pilot flame for enabling the supply of fuel mixture to the burner after the detection of the presence of the pilot flame.
It is therefore a general object of the present invention to provide a new and improved fluid bed furnace which includes a new and improved pilot light assembly which provides a pilot flame of substantial expanse within the fluid bed above the fluidizable material and which includes means for sensing the presence of the pilot flame to enable the supply of the fuel mixture to the furnace burner subsequent to such detection.